Various techniques exist to “image” internal physiology. Some of these techniques are considered “non-invasive”, for example, those that rely on penetration of sound (e.g., ultrasound), electromagnetic energy (e.g., MRI, CT) or particles (e.g., PET). However, when such techniques require enhancement, clinicians often resort to intravenous delivery of contrast agents or dyes. For example, cardiac fluoroscopy can be enhanced through use of contrast agents or dyes delivered intravenously via a catheter. Further, fluoroscopy also provides some degree of visualization, which can help a clinician navigate such a catheter in a patient's body.
Another non-invasive technique is often referred to as “electrical impedance tomography” or “electrical capacitance tomography”. Such techniques are referred to herein as simply “electrical tomography” (ET). Conventional ET generates images of the body related to dielectric properties and underlying physiology as reconstructed from skin-surface electrical measurements. Typically, ET involves placing electrodes on the skin and applying small alternating currents via some or all of the electrodes. In turn, corresponding electrical potentials are measured and processed to generate an image or images that represent the underlying physiology.
An invasive variation of ET is referred to herein as ET localization where one or more electrodes are introduced into the body and relied upon for physiologic mapping or localization (e.g., via delivery of electrical potentials or current, measurement of potentials or current, etc.). A particular commercially available navigation and localization system is marketed as the ENSITE® NAVX® system and technology (St. Jude Medical, Inc., Minnesota).
In a typical clinical application, the ENSITE® NAVX® system drives current across three pairs of body surface patches to create a Cartesian coordinate system in the body, in which indwelling electrodes may be located in real-time. Potentials sensed by the indwelling electrodes in the current fields can be used to compute impedances that determine a position of each electrode (e.g., in three dimensions). In various clinical applications, indwelling electrodes may be used to measure cardiac potentials and to deliver energy, for example to pace or to ablate tissue. A computed position or positions of an indwelling electrode or electrodes, in conjunction with the sensed electrograms and possibly other information, can be used to generate maps that may include anatomical features as well as information about tissue substrate and performance.
Various exemplary technologies described herein pertain to localization, navigation or both localization and navigation. Various examples are described with respect to ET. As described in below, various exemplary technologies may be optionally suited or adapted for use with imaging modalities such as MR, CT and ultrasound (e.g., ultrasound tomography, UT).